In some wireless communications systems, the total available bandwidth in a given cell or sector may be partitioned into different frequency bands, e.g., distinct frequency bands. In addition, the total available bandwidth in a given cell or sector may vary throughout the system.
Typically, the known available bandwidth in a given cell or sector is partitioned to include a number of frequency bands, each band in the system having the same bandwidth, basic structure, and timing so that the wireless terminals can readily establish connections, perform communications, and execute hand-off operations with the various base stations throughout the system. When, the available bandwidth (BW) in a given cell or sector is partitioned, in addition to the fixed size frequency bands, there may be left over unused frequency bandwidth that is currently wasted.
FIG. 1 includes a drawing 100 illustrating exemplary partitioning of BW in an exemplary code division multiple access (CDMA) system and a drawing 150 illustrating exemplary partitioning of BW in an exemplary orthogonal frequency division multiplexing (OFDM) system. In drawing 100, the available BW, e.g., 5 MHz, 102 is partitioned to include three 1.25 MHz BW bands (104, 106, 108), each associated with a carrier frequency (fA 110, fB 112, fC 114), respectively. CDMA signaling (116, 118, 120) is associated with (fA 110, fB 112, fC 114), respectively. Regions 122 and 124 represent signaling overlap from adjacent bands. Regions 126, 128 represent regions of boundary areas, which have been established within the allocated 5 MHz band 102 to limit interference to outside adjacent bands. In CDMA systems, due to the characteristics of the CDMA signals and the power shaping filters used for each band (104, 106, 108) the 1.25 MHz bandwidth associated with the composite of the regions 126, 122, 124, and 128 is used and generally needed to: (i) limit interference levels between adjacent bands (104, 106, 108) thus allowing for reliable operation in the system and (ii) prevent the signaling from (116, 120) from encroaching on adjacent bands outside of the allocated 5 MHz band 102, which may be allocated to a system operated by a different service provider.
In drawing 150, the available BW, e.g., 5 MHz, 152 is partitioned to include, e.g., three 1.27 MHz BW bands (154, 156, 158). OFDM signaling within band 154 includes signals communicated on OFDM modulation symbols using, e.g., 113 evenly spaced tones (tone 1 160, tone 2 162, tone 3 164, . . . tone 113 166). The inter-tone spacing (184, 186) is the same between each tone, e.g., 11.25 KHz. The inter-tone spacing of 11.25 kHz also represents the bandwidth allocated to a single tone. Similarly, OFDM signaling within band 156 includes signals communicated on OFDM modulation symbols using, e.g., 113 evenly spaced tones (tone 1 168, tone 2 170, tone 3 172, . . . tone 113 174). The inter-tone spacing (188, 190) is the same between each tone, e.g., 11.25 KHz. Similarly, the OFDM signaling within band 158 includes signals communicated on OFDM modulation symbols using, e.g., 113 evenly spaced tones (tone 1 176, tone 2 178, tone 3 180, . . . tone 113 182). The inter-tone spacing (192, 194) is the same between each tone, e.g., 11.25 KHz. With OFDM signaling, unlike CDMA signaling, quite sharp power shaping filters can be used due to the nature of the OFDM signals. Drawing 150 shows three exemplary power shaping filters (151, 153, 155), each associated with a bandwidth only slightly larger than 1.27 MHZ (157, 159, 161), respectively. This leaves a remaining unused bandwidth of slightly less than 1.19 MHz, as represented by the composite of regions 163, 165, 167, and 169. This amount is less than the standard size of 1.27 MHz needed for an additional standard band, yet sizeable.
In the exemplary OFDM system, the remainder unused bandwidth may be a result of the exemplary 5 MHZ system being different than what the system was originally designed. For example, the exemplary OFDM system may have been originally designed for distinct bandwidth allocations of approximately 1.27 MHz.
In view of the above, there is a need for methods and apparatus, particularly in OFDM systems, that increase or maximize the use of available allocated bandwidth. Methods and apparatus that flexibly allow for adaptations to changes in available bandwidth would be beneficial. Changes could be in response, e.g., to additional bandwidth licensed to a service provider or to dynamic redeployments of bandwidth to meet current user needs. In addition, designs that allow wireless terminals (WTs) to readily adjust to use different amounts of bandwidth in different sectors and/or cells of the same system would be advantageous. In such multiple bandwidth OFDM systems, there is also a need for efficient methods and apparatus to communicate from a base station to the WTs the bandwidth and/or structure associated with the cell and/or sector.